Cultivation Insight Into Grass Weed Strategies
25 July 2024, UK: Unprecedented levels of ryegrass and other grass weeds can be found in many cereal fields this season. Maps and records of populations of grass weeds gained prior to harvest will help to make decisions on autumn establishment techniques that could mitigate future problems, advocates Syngenta grassweed specialist, Georgina Young.
Last year’s difficult establishment season, followed by the record-breaking wet spring, severely hampered herbicide strategies for most growers. NIAB trials have shown it will be the uncontrolled early established grass weeds from last autumn, that are most likely to produce very large numbers of highly viable seeds this summer, she warns.
“Farmers and agronomists are likely to need the full range of integrated control measures to tackle the issues this autumn.
“With the significant switch to min-till or direct drill establishment over recent seasons, the majority of weed seeds in those fields will still be close to the surface. While the older seeds that have remained undisturbed in the soil profile will have declined in viability.
“Now there is the real chance to bury this year’s high seed burden using traditional plough cultivations, and bring a clean seedbed up to the surface.”
“Identifying weed populations will enable growers to focus the more costly and time-consuming inversion tillage reset on the most appropriate fields”, Georgina suggests.
This season growers and agronomist can use the Cultivations Insight Tool to calculate where grass weeds seeds are likely to end up over successive seasons of different establishment techniques.
“The model draws on data from multiple years of Syngenta grassweed trials using a range of establishment systems,” she explains.
“Factoring in what has happened in an individual field over previous years, can help decide where a different approach could have the greatest benefit this autumn.
“The trials have revealed the immense benefit that can be obtained in a single year reset with the plough in a high grass weed burden situation, especially where that is followed by spring cropping.”
Selecting which cultivation system is most appropriate for individual fields and grass weed situations will also have an implication for drilling dates, points out Georgina.
“All the evidence from repeated years of Syngenta grass weed research indicates later drilling – leaving more time to remove the early germinated grass weeds – is a highly successful part of the control strategy.”
“But that clearly has to be balanced against the demands to get crops in the ground in the available autumn window, which will be different for every farm’s situation.”
It is also likely to an impact on herbicide strategy, since earlier drilling may require greater emphasis on a sequence of pre- and post-emergence applications required to cope with a more protracted and potentially more intense grass weed burden, compared to later established crops.
“Any pre-emergence application is likely to have to deal with a high weed population, along with the potentially extended period of control if weather and soil conditions again disrupt follow-up treatments.”
DEFY is a flexible option which can be incorporated into a robust pre-emergence herbicide stack to enhance the overall efficacy, or can be utilised post emergence in a follow up spray to enhance the persistence of the overall program.
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